1. Field of the Invention
This invention relates to bearing assemblies, and more particularly to ball track bearing assemblies that reduce friction associated with movement of two bodies relative to each other.
2. Description of the Related Art
Bearing assemblies may be of the type which support a carriage or block for movement along a support member such as an elongated shaft, rail or spline to reduce friction associated with longitudinal or rotational motion. These bearing assemblies can be of the open or closed type.
Bearing assemblies also contemplated by the present invention generally include an outer housing and a block dimensioned for insertion into the outer housing. The block defines a plurality of longitudinal planar faces each having at least one ball track in a loop configuration for containing and recirculating bearing balls. The ball tracks include open portions which facilitate load transfer from the supporting shaft to load bearing structure such as ball retainers operatively associated with either the block or the outer housing. Return portions of the ball tracks permit continuous recirulation of the bearing balls through the ball tracks during linear motion. The block is typically formed as a monolithic element with the ball tracks integrally incorporated therein. See, U.S. Pat. No. 3,767,276 to Henn. This structure, however, is difficult to efficiently manufacture because of the complex molds required. In particular, the ball tracks are incorporated into the molds and the ball tracks may require further machining operations for precise alignment and tolerances of the ball tracks for proper recirulation of the bearing balls.
Linear motion recirculating bearing assemblies having multiple tracks for longitudinal movement along a shaft are known in the art. See, for example, U.S. Pat. Nos. 4,181,375, 4,293,166, 4,463,992 and U.S. Pat. No. 3,545,826 entitled Compliant and Self-Aligning Ball Bearing for Linear Motion. These bearing assemblies are typically characterized by a housing which forms a plurality of tracks arranged in radial planes with respect to the longitudinal axis of the shaft. Each of the tracks has a load-bearing path wherein the roller elements contact the shaft and a radially spaced return path for serially recirculating the roller elements back to the load-bearing path. Turnarounds are positioned at each axial end of the tracks to interconnect the load-bearing and return paths. These bearing assemblies, particularly the assembly shown in the '992 patent, are even more difficult to manufacture because a plurality of ball tracks are being formed.
A plurality of individual axial guides are commonly provided in conjunction with the load bearing paths to guide and separate the rolling elements in the load bearing paths. These axial guides are usually in the form of separate axially extending elements which are individually placed between the end caps at the axial ends of the bearing assembly. Similarly, a plurality of individual inner guides may be positioned at each of the inner axes of the turnarounds to guide the roller elements from the load-bearing tracks to the return tracks. Both the axial guides are the inner guides usually must be individually and separately positioned within the bearing assembly. This technique is both time consuming and inefficient.
In addition to the problems associated with assembling and positioning the axial and inner guides, bearing assemblies making use of typical individual bearing plates tend to have alignment and positioning problems associated therewith. These bearing plates are usually positioned longitudinally over the load bearing tracks and serve to transmit loads from the carriage, through the roller elements, to the shaft. If these bearing plates are not properly and securely positioned, the bearing assembly will not operate efficiently and may cause binding and/or misalignment of the rolling elements.
These designs for such linear bearing assemblies have some inherent drawbacks. For example, in the bearing of U.S. Pat. No. 4,717,264, the raceway rail has a load bearing surface and a single return surface, both formed in a lower side of the raceway rail. This arrangement does not make efficient usage of the space surrounding the rail and inhibits the placement of an optimum number of load-bearing paths for a given surface area. Also, the ball turnaround structure creates a tight arc for reversal which limits the speed capacity and can result in stagnation of ball movement through the ball path.
These bearing assemblies may be used, for example, with rack and pinion steering devices in automobiles. The steering assembly is normally of the rack and pinion type, running transverse to the axis of the vehicle. The pinion is typically loaded against the rack, such that there is a force transmitted between the rack shaft and the bottom of the housing. In rack and pinion steering gears, a rack bar transverses along its axis when the pinion, which has teeth meshing with the teeth of the rack bar, is turned by the steering wheel and column assembly. Commonly, a support yoke biases the rack bar, toward the pinion to maintain the desired meshing of the rack teeth with the pinion teeth during rotation of the pinion. The support yoke also reacts against shock loads transmitted to the rack bar from bumps in the road via the vehicle wheels, suspension and steering system tie rods.
In the past, attempts have been made to reduce the friction that results in this reaction, usually through the application of low-friction materials utilized in a known fashion. Friction can be reduced by applying low friction surface coatings to the constituent parts. Minimization of friction is an important factor for achieving a good steering feel facilitating safe driving conditions. In particular, in the case of a power failure, reducing friction allows a driver to steer a vehicle without loss of control of the vehicle. Bearing assemblies utilizing bearing balls have a particularly advantageous application with steering devices because they provide a smooth travel of the parts relative to one another.
It is highly desirable to have a bearing assembly having at least one rolling element track configured to reduce friction associated with movement of two bodies relative to each other in a low cost application of rolling element technology.
Accordingly, it is one object of the present invention to provide a bearing assembly having at least one rolling element track that facilitates recirulation of bearing balls for reducing friction associated with the movement of two bodies relative to each other.
It is a further object of the present invention to provide a bearing assembly including rolling element tracks having an efficient arrangement of load bearing and return paths to optimize quantities of rolling elements in the tracks.
It is another object of the present invention to provide a bearing assembly which is easily and efficiently manufactured and assembled.
These and other high desirable objects are accomplished by the present invention in a bearing assembly having rolling element tracks that facilitate recirulation of bearing balls disposed herein for reducing friction associated with movement of two bodies relative to each other in a low cost application of rolling element technology.
Objects and advantages of the invention are set forth in part herein and in part will be obvious therefrom or may be learned by practice with the invention, which is realized and attained by means of instrumentalities and is combinations pointed out in the appended claims. The invention comprises the novel parts, construction, arrangements, combinations, steps and improvements herein shown and described.